The objective of this study is to determine how flavin dehydrogenases interact with the membrane-bound electron transport chain in Salmonella typhimurium. This work will focus on two main topics: 1. Regulation of the put operon. The put operon has a unique control mechanism that seems to be mediated by the putA gene product, proline oxidase. When exogenous proline is available, proline oxidase binds to the membrane where it functions as flavin dehydrogenase; but in the absence of proline, it accumulates in the cytoplasm where it acts as an autogenous repressor. Determining how proline oxidase controls its own expression may help us understand how other membrane-bound regulatory proteins work. In addition, the regulatory properties of putA mutations provide a genetic selection for membrane interaction mutants. 2. Flavin dehydrogenase-membrane interactions. Flavin dehydrogenases must associate with specific membrane sites in order to interact properly with the electron transport chain. However, it is not known what component(s) of the electron transport chain they interact with directly or even how they interact with the membrane. Genetic studies on the interaction of flavin dehydrogenases with the electron transport chain will provide a novel approach for understanding how proteins interact with membranes in vivo. All of the components involved and the specific interactions required can be defined by isolating and characterizing two unique classes of dehydrogenase mutations: mutations that prevent the dehydrogenase from interacting with the membrane but don't eliminate enzymatic activity of the dehydrogenase in vitro, and mutations that alter with dehydrogenase so that it can still bind the membrane but can't properly interact with the electron transport chain. Genetic and biochemical analysis of these mutants will indicate what membrane component(s) directly interact with flavin dehydrogenases and what kinds of interactions are required between flavin dehydrogenases and the membrane electron transport chain. Such mutants should provide insight into the general biological problem of how peripheral membrane proteins interact with the membrane.